<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text">
<input type="button" value="平方" onclick="f()">
<input type="button" value="求和" onclick="f()">
<div>结果</div>

<script>

    let d=document.querySelector("div");
    let i=document.querySelector("input")
    function  f(){
        d.innerText="结果:"+(parseFloat(i.value)+parseFloat(i.value));
    }

    function f(){
        if (isNaN(i.value)){
            d.innerText="输入结果错误!"
            return
        }
        d.innerText="结果:"+i.value*i.value;
    }
</script>

</body>
</html>